Anti-roll-back device

ABSTRACT

A device (10) allows forward (clockwise) rotation of a shaft (12) but prevents reverse rotation unless disengaged. A loop (20) is attached at one end to a slide show (16), passes round a drum (14) on the shaft (12), around a first pin (24) and a second pin (26), to an arm (28). The arm (28) can move clockwise to slacken the loop (20) to disengage the device (10) and allow rotation of the shaft (12) in either sense. A mechanism for controlling the arm (12) and for self-tightening the loop (20) is described.

The present invention relates to anti-roll-back devices for theselective prevention of reverse rotation of a rotatable member, andparticularly but not exclusively for a device for use in vehicles.

When a vehicle is on an inclined road and facing uphill, the handbrakemay not hold the vehicle against rolling back, particularly if thevehicle is heavy or heavily laden. Furthermore, when the vehicle is onlytemporarily brought to a halt, many drivers do not apply the handbrakebut hold the car against rolling back by partially engaging the clutchto a degree sufficient to hold the vehicle stationary. This causesunnecessary wear of the clutch plates.

One proposal to overcome this problem uses a loop or noose which extendsfrom an anchor point around a rotatable member such as the vehicle driveshaft, to a further anchor point. The arrangement is such that when thedrive shaft is rotating in the forward direction of the vehicle, theloop or noose remains slack around the shaft, but as soon as the shaftattempts to rotate in the reverse direction, the loop or noose tightenson the shaft to prevent that reverse rotation. In order to enablereverse rotation when that is required, an arrangement is provided whichis selectively activatable to prevent the loop or noose tightening onthe shaft during reverse rotation. Conveniently, the arrangement isactivated when reverse gear is selected.

The present invention seeks to provide an improved device of the typedescribed above.

According to one aspect of the invention, there is provided ananti-roll-back device for a rotatable member, comprising a second memberlocated adjacent the rotatable member, a loop or noose secured at oneend to the second member and extending around the rotatable member topass around a guide member secured to the second member, the loop ornoose then extending to a movable member, and there being releasablelocking means operable to hold the movable member against movement andto release the movable member to move as and when required.

The movable member may be a pivotal member. The pivotal member may bemounted on a pivot located in fixed spaced relationship to the rotatablemember.

The loop or noose may be anchored to the pivotal member.

Preferably the locking means incorporate bias means operable to providea bias force to cause or assist in movement of the movable member. Thebias means may comprise a resilient member.

The locking means may comprise a remotely controllable actuator, such asa solenoid. The actuator preferably controls a latch means operable toprevent the movable member moving.

The movable member may be coupled to the locking means by at least oneintermediate member. Preferably the latch means acts directly on the orone of the intermediate members. The movable member may be directlycoupled to a first intermediate member to cause the first intermediatemember to move as the movable member moves. The first intermediatemember may comprise first and second levers mounted on a common spindle,the movable member being coupled to the first lever and the lockingmeans being coupled to the second lever. The coupling between themovable member and the first intermediate member may comprise a pin inthe lever or member, and a slot or recess in the member or lever,respectively. Preferably the first intermediate member is directlycoupled to a second intermediate member. The coupling may be by means ofa pin slidable in a slot or recess. The locking means is preferablycoupled directly to the second intermediate member. The secondintermediate member may be pivotally mounted. The locking means maycomprise a latch bar movable into and out of engagement with acorresponding formation on the second intermediate member.

The device may comprise manually operable means for releasing thelocking means. The manually operable means may comprise a control memberoperable to move the latch bar. The control member may comprise a Bowdencable.

Preferably, when the locking means is engaged, the movable member isheld in a position such that the rotatable member Can freely rotate inone (forward) direction, but immediately the rotatable member attemptsto rotate in the opposite (reverse) direction, a force is appliedthrough the loop or noose to urge the second member in a direction tocause the loop or noose to tighten on the rotatable member and preventopposite (reverse) rotation.

Preferably, when the locking means is disengaged, a force applied to theloop or noose by rotation of the rotatable member in the reversedirection provides a force on the loop or noose to cause the movablemember to move to slacken the loop or noose. Preferably the loop ornoose is maintained in a slack condition until a first (forward)rotation of the rotatable member recommences.

The apparatus may further comprise second bias means operable to biasthe second member to lightly tighten the loop or noose around therotatable member.

The loop or noose may pass around a further guide member between theguide member secured to the second member and the pivotal member, thefurther guide member being fixed in relation to the rotatable member.

The device may further comprise a wear member carried by the slidablemember to bear on the rotatable member and maintain a minimum spacingbetween the second member and the rotatable member.

A difficulty with this type of device may arise as a consequence of theheavy loads transmitted to the loop or noose when holding the shaftagainst rotation, especially if the vehicle is on a steep hill or isheavy. There is a tendancy for the loop or noose to stretch in use. Thisseriously impairs the action of the loop or noose, reducing theeffectiveness of the device in preventing the vehicle from rolling back.

According to a second aspect of the invention there is provided ananti-roll-back device, comprising a loop or noose which extends, in use,from an anchor location, around a rotatable member to another anchorlocation, and further comprising control means selectively activatableto put the loop or noose in a first or second operative conditionwherein, in the first operative condition, the rotatable member canrotate in a first forward direction, the loop or noose tightening on therotatable member as it attempts to rotate in a second reverse directionto prevent rotation in the reverse direction, and wherein in the secondoperative condition the loop or noose allows the rotatable member torotate in the reverse direction, the device further comprising an anchorarrangement located at one of the anchor locations and operableindependently of the operation of the control means to take up slack inthe loop or noose, arising from stretching of the material thereof, theanchor arrangement being lockable to prevent the loop or noose fromslackening.

Preferably the anchor arrangement comprises a rotatable anchor member towhich the loop or noose is secured, whereby rotation of the anchormember causes part of the loop or noose to be wound on to the anchormember to take up slack. The rotatable anchor member is preferably a pinmember. The apparatus may further comprise a resilient member whichprovides a force tending to cause the anchor arrangement to operate totake up slack, whereby any slack which occurs will automatically betaken up. The resilience of the resilient member is preferablysufficient to cause the loop or noose to be tightened into light contactwith the rotatable member. The resilient member may provide a force to apivotally mounted lever forming part of the anchor arrangement, therebytending to cause the lever to pivot to operate the anchor arrangement.

Preferably the operation of the anchor arrangement causes rotation of aratchet, and the arrangement further comprising a pawl which, in use,cooperates with the ratchet to prevent the loop or noose fromslackening.

The anchor arrangement may be adapted to allow manual operation to takeup slack.

Preferably the device further comprises a second member slidably mountedin close proximity to the rotatable member, the loop or noose beinganchored to the slidable member and extending around the rotatablemember, around a guide member attached to the slidable member, and to asecond anchor location.

Preferably the anchor arrangement is mounted on the slidable member toanchor the loop or noose thereto.

The invention also provides an anti-roll-back device according to thesecond aspect of the invention, and incorporating any or all of thefeatures of the first aspect of the invention.

Examples of anti-roll-back devices according to the present inventionwill now be described in more detail, by way of example only, and withreference to the accompanying drawings in which:

FIG. 1 is a front elevation of a first device when engaged to preventreverse rotation;

FIG. 2 corresponds to FIG. 1, but shows the device when disengaged;

FIG. 3 is a rear elevation corresponding to FIG. 1, with the rotatablemember removed, for clarity;

FIG. 4 is a rear elevation corresponding to FIG. 2, with the rotatablemember removed, for clarity;

FIG. 5 is a front elevation corresponding to FIG. 1, showing a secondanti-roll-back device which embodies the present invention;

FIG. 6 is an elevation view of the slidable member shown in FIG. 5, toan enlarged scale;

FIG. 7 is a side view of the slidable member of FIG. 6; and

FIG. 8 is a partial section of FIG. 7, along the lines 8--8.

Turning to FIG. 1, there is shown a device 10 operable, when engaged, toallow forward rotation of a rotatable member or shaft 12 but to preventreverse rotation of the shaft 12.

The device 10 Comprises a drum 14 mounted to rotate with the shaft 12. Asecond member or slide shoe 16 is located close to the drum 14, butmaintained at a minimum distance from the drum by phosphor bronze wearpads 18 which are mounted on the slide shoe 16, and bear lightly on theouter surface of the drum 14 attached to the shaft 12.

A loop or noose 20 (hereafter referred to simply as a loop) is attachedat one end to the slide shoe 16 by means of an attachment arrangementindicated generally at 22. The loop 20 passes around the drum 14, undera pin 24 rotatably mounted on the slide shoe 16, over a rotatable pin 26which is fixed relative to the shaft 12, and to a pivotal arm 28. Therotatable pins 24,26 could alternatively be replaced by fixed pinscarrying rotatable collars.

The arm 28 is pivotally mounted at an axis 30. The loop 20 passes aroundthe free end 32 of the arm 28 and is anchored to the arm 28 by means ofwashers 34 and a screw 36.

The attachment arrangement 22 consists of a post 38, a bar 40, and atleast one screw 42 which holds the bar 40 against the post 38. The freeend of the loop 20 passes between the bar 40 and post 38. The post 38 ismounted on the slide shoe 16. Consequently, by tightening the screws 42,the free end of the loop 20 is firmly secured to the slide shoe 16.

A light spring 44 is attached at one end to the slide shoe 16 and at itsother end, to a fixed position. The spring 44 lightly pulls on the slideshoe 16. This biasses the pin 24 away from the pin 26 which in turnincreases the path length of the loop 20 from the arm 28 to theattachment arrangement 22 and consequently maintains the loop 20 inlight contact with the drum 14.

When the device 10 is in the condition shown in FIG. 1, any forwardrotation of the shaft 12 (in the clockwise direction) creates africtional force between the loop 20 and the drum 14. The direction ofthis force is to move the slide shoe 16 up (in the FIG. 1 orientation).This causes the pin 24 to approach the pin 26 and reduce the overallpath length of the loop 20, so that the loop slackens and does notinterfere with the forward rotation. However, if the shaft 12 begins torotate in reverse (anti-clockwise) the friction on the loop pulls theslide shoe 16 in the opposite direction. The pin 24 moves away from thepin 26 and the loop 20 tightens around the drum 14. The tighter the loop20 becomes, the greater is the frictional force pulling the pin 24 awayfrom the pin 26 and consequently, the shaft 12 is tightly held againstreverse rotation. To assist this, the loop 20 may be a belt of highfriction material. Furthermore, although the shoe 16 is located betweenthe arm 28 and the drum 14, it is otherwise unrestricted in itsmovement. The shoe will tend to slide on the drum between the twopositions shown in the drawings, but this freedom allows the shoe tomove to other positions, reducing the risk of jamming. The term "slideshoe" is therefore not intended to imply that the shoe can only move bysliding.

In some applications, reverse rotation will sometimes be required. Forinstance, when the device is installed in a vehicle, the device canprevent the vehicle rolling downhill (when facing uphill) but thevehicle will occasionally need to be reversed. It is therefore necessaryto be able to disengage the device. The FIGS. 3 and 4 show a controlmechanism for the device. The control mechanism operates to controlpivotting of the arm 28 between the positions shown in FIGS. 1 and 2.The shaft 12 and drum 14 are omitted from FIGS. 3 and 4, in theinterests of clarity.

The arm 28 is pivotal from the engaged position shown in FIG. 1 to thedisengaged position shown in FIG. 2, as has been described; The free end32 carries a pin which runs in a slot 46 in a first lever 48 of anintermediate member which is pivotally mounted at 50. As the arm 28moves from the engaged position to the disengaged position, the pin atthe free end 32 moves from one end of the slot 46 to the other end, andthe lever 48 pivots about the axis at 50.

The pivotal mounting of the lever 48 is by means of a spindle 50 whichpasses through the base plate 52 of the device 10, through to the rearwhere the spindle 50 carries a second 1ever 54 having 1ever arms 54A and54B.

A second intermediate-member 56 is pivotally mounted at 58 at the rearof the base plate 52. A curved slot 60 is provided along the member 56and engages a pin (at 62) carried on the second 1ever arm 54A. Inconsequence, the second 1ever 54 cannot pivot unless the secondintermediate member 56 is free to pivot. If the second lever 54 is notfree to pivot, the first lever 48 is not free to pivot. If the firstlever 48 is not free to pivot, the arm 28 is not free to pivot. If thearm 28 is not free to pivot, the loop 20 cannot slacken and the deviceis held in the engaged position.

The second intermediate member 56 is normally held against movement bymeans of a latch arrangement at 64. This consists of a latch arm 66pivotally mounted at 68 and having a notch 70 which can engage a pin 72carried on the second intermediate member 56, or can release the pin 72by pivotting about the axis 68. The position of the latch arm 66 andhence the engagement or disengagement of the notch 70 and pin 72 iscontrolled by a solenoid actuator 74. The solenoid 74 has a returnspring 76 which normally holds the latch arm 66 in the position shown inFIG. 3, in which the notch 70 is engaging the pin 72 to prevent movementof the second intermediate member 56. As described above, this locks thedevice 10 in the engaged condition.

If reverse rotation of the shaft 12 is required, current is supplied tothe solenoid 74 to push the latch arm 66 to the position shown in FIG.4, releasing the pin 72 from the notch 70. The intermediate member 56 isnow free to pivot and this movement will occur in the followingcircumstances. With the latch disengaged, if the shaft 12 begins torotate in the reverse direction, the loop 20 pulls on the arm 28, urgingit to the disengaged position shown in FIG. 2. In moving to thedisengaged position, the arm 28 pulls the first lever 48 and thus thesecond lever 54 pivots to the position shown in FIG. 4. In order for thesecond lever 54 to move to this position, the second intermediate member56 also pivots, again to the position shown in FIG. 4.

This pivotal motion of the second lever arm 54 and second intermediatemember 56 is resisted by return spring 78 (shown in FIG. 3 but not inFIG. 4), between the second lever arm 54b and the pivot of the latch arm66, and a spring 80 between the second intermediate member 56 and afixed point 82. The action of these springs is to urge the variousmembers back to the positions shown in FIG. 3, but while the shaft 12 isin reverse rotation, the forces through the loop 20 override the springs78,80 to maintain the members in the position shown in FIG. 4.

The solenoid 74 will normally be activated by a switch associated with agear lever, so that when reverse gear is selected, the locking mechanismis released to allow the device to disengage. Consequently, when reversegear is deselected, the solenoid 74 returns the latch arm 66 to theoriginal position (FIG. 3) by action of the spring 76. However, themembers 54,56 will still be in the positions shown in FIG. 4 and the pin72 will be out of the notch 70. This condition will continue whilereverse rotation of the shaft 12 continues (reverse rotation maycontinue after reverse gear is disengaged). As soon as forward rotationagain occurs, the loop 20 will tend to slacken around the drum 14, asdescribed above. This slackness allows the springs 78, 80 to return themembers 54,56 to the positions shown in FIG. 3, and in so doing, the pin72 re-enters the notch 76 to lock the device once again in the engagedcondition.

In case it is necessary to manually override the device 10, a Bowdencable 84 is provided. The sleeve 86 is attached to the base plate 52 at88. The cable 90 of the Bowden cable 84 passes round a drum 92 to thelatch arm 66 to which it is secured. Consequently, by operation of theBowden cable 84, the latch arm 66 can be pulled to disengage the pin 72.Manual override may be required if, for instance, the solenoid fails, orduring routine maintenance.

Various modifications can be made to the apparatus described above,without departing from the scope of the present invention. Inparticular, various different actuator and locking arrangements could beused and other arrangements could be devised for coupling the lockingmeans to the pivotal arm 28. The geometry off the loop 20 could bevaried, with consequent changes to the location of guide pins and theshape of the slide shoe 16.

The remaining FIGURES show a modified version of the device 10 shown inFIGS. 1 to 4. The anti-roll-back device 110 is again of the form inwhich a loop or noose 112 (hereafter referred to simply as a loop)extends from an anchor location at 114 around a guide member 116 in theform of a pin, around a second guide member 118 in the form of a secondpin and then around a drum 120 on the drive shaft 122 to a second anchorlocation at 124. The anchor arrangement at 124, and the pin 118 are bothmounted on a second member 126 (referred to as a slide shoe). The slideshoe 126 can slide up and down (in the orientation shown in FIG. 5). Ifthe shaft 122 rotates in the forward direction (clockwise) frictionbetween the drum 120 and the loop 112 causes the slide shoe 126 to rise.This in turn slackens the loop 112 to reduce any frictional engagementbetween the loop 112 and the drum 120, thereby allowing free forwardrotation. If the shaft 122 begins to rotate in the reverse direction(anti-clockwise) frictional engagement between the drum 120 and the loop112 pulls the slide shoe 126 down. This causes the pin 118 to move awayfrom the pin 116, thereby increasing the overall path length of the loop112 from the anchor point 114 to the anchor arrangement at 124. Thiscauses the loop 112 to tighten on the drum 120 to prevent furtherreverse rotation. The movement of the shoe 126 is described as"sliding", but it can be seen from FIG. 5 that the movement isprincipally determined by the forces applied by the loop 112 to theanchor point 124 and pin 118. This reduces the risk of jamming.

In order to allow the device 110 to be overriden, the anchor location114 is on a rotatable arm 128 which corresponds to the arm 28 of FIGS. 1to 4, and can pivot about an axis at 130 in a clockwise direction, toslacken the loop 112 sufficiently to avoid the loop 112 engaging andpreventing rotation of the drum 120.

The arrangement so far described in relation to FIG. 5 correspondsclosely to the arrangement described in relation to FIGS. 1 to 4. Theposition of the arm 128 is controlled by a control mechanism which isnot wholly visible in FIG. 5, being mainly located behind the plate 132.The control mechanism controls the arm 128 by means of a rotatable shaft133 extending through the plate 132, and carrying a lever 131corresponding to the lever 48 of FIG. 1. Other details of the controlmechanism may be the same as those described above in relation to FIGS.1 to 4, or alternative control mechanisms could be used.

The slide shoe 126 and the anchor arrangement at 124 can be described inmore detail with reference to FIGS. 6, 7 and 8. The slide shoe 126 has afront plate 134 and a rear plate 136. The pin 118 extends between theplates 134,136 and is either rotatably mounted thereon, or carries arotatable sleeve. The pin 118 is near the upper end of the shoe 126.

The anchor arrangement 124 is near the lower end of the shoe 126. Theanchor arrangement comprises a pin 138 which is rotatably mounted on theplates 134,136 and has a diametric slot 140 extending substantially thewhole length of the pin 138 between the plates 134,136. One end of theloop 112 is secured to the pin 138 by passing it through the slot 140,doubling it back around a securing pin 142 (FIG. 8) and passing the freeend 144 back through the slot 140. Any rotation of the pin 138 willcause the loop 112 to wind onto or off the pin 138.

An extension 146 of the pin 138 passes through the front plate 134 andcarries a ratchet 148 and a lever 150. The free end of the lever 150 isattached to one end of an extension spring 152, the other end of whichis attached to a post 154 mounted on the front plate 134. The lever 150and spring 152 are not shown in FIG. 5, in the interests of clarity.

The spring 152 is normally under tension, as can be seen from FIG. 6,and this applies a force to the lever 130 tending to rotate the leverand hence the pin 138 in the anti-clockwise direction (FIG. 6). Reverserotation of the ratchet 148, in the clockwise direction, is prevented bya pawl 156 which is rotatably mounted at 158 and urged against theratchet 148 by the action of a second extension spring 160 actingbetween the pawl 156 and the post 154. The rotatable mounting of thepawl 156 is provided by a further pin 162 which extends between theplates 136 and through the front plate 134 to carry the pawl 156 at oneend.

In order to set up the device 110 for use, the pin 138 is turned to windthe loop 112 on to the pin 138 until the loop 112 is in light contactwith the periphery of the drum 120, but not in sufficiently tightcontact to prevent forward rotation of the shaft 122. The spring 152applies a force to the pin 138 through the lever 150, to maintain thislight contact. The device 110 can then be used normally, as describedabove, to allow forward rotation and prevent reverse rotation of theshaft 122, or to be disengaged by pivotal movement of the arm 128, toallow reverse rotation.

Initial setting up of the device is facilitated by a nut 164 adjacentthe ratchet 148. The nut 164 allows the ratchet 148 and pin 138 to berotated manually, for instance by means of a spanner.

If the loop 112 stretches, as a result of the large forces applied to itduring use, the loop 112 would become slack. This slackness allows thespring 152 to pull the lever 150 towards the post 154, thereby rotatingthe pin 138 to coil more of the loop 112 on to the pin 138, so taking upthe slack caused by the stretching. Consequently, the slackness isautomatically taken up to maintain the loop 112 in the adequately tightcondition. Reverse rotation of the pin 138, so as to slacken the loop112, is prevented by the locking action of the pawl 156.

Variations and modifications can be made to the apparatus describedabove in relation to FIGS. 5 to 8, without departing from the scope ofthe present invention. It is possible to envisage the self-tighteningarrangement of the anchor location at 124 being incorporatedalternatively in the anchor location at 114. Other arrangements could beused to take up slack. Other spring arrangements could be adopted, andlocking means alternative to the ratchet and pawl arrangement could beused.

It has been found that it may be advantageous when fitting a new orreplacement loop to lightly roughen or serrate the part of the drumwhich contacts the loop. This allows better grip for the new loop untilit has time to "bed in".

The terms "upper" "lower" etc. have been used above in accordance withthe orientation of the device shown in the drawings, but it is to beunderstood that the device could be used with other orientations.

Whilst endeavouring in the foregoing specification to draw attention tothose features of the invention believed to be of particular importanceit should be understood that the Applicant claims protection in respectof any patentable feature or combination of features hereinbeforereferred to and/or shown in the drawings whether or not particularemphasis has been placed thereon.

I claim:
 1. An anti-roll-back device for a rotatable member, comprisinga second member located adjacent the rotatable member, a loop or noosesecured at one end to the second member and extending around therotatable member to pass around a guide member secured to the secondmember, the loop or noose then extending to a movable member, the secondmember being substantially unrestricted in its movements in response toforces applied to it, during use, by said loop or noose, and there beingreleasable locking means operable to hold the movable member againstmovement and to release the movable member to move as and when required.2. A device according to claim 1, wherein the movable member is coupledto the locking means by at least one intermediate member.
 3. A deviceaccording to claim 2, wherein the movable member is directly coupled toa first intermediate member to cause the first intermediate member tomove as the movable member moves.
 4. A device according to claim 3,wherein the first intermediate member comprises first and second leversmounted on a common spindle, the movable member being coupled to thefirst lever and the locking means being coupled to the second lever. 5.A device according to claim 4, wherein the coupling between the movablemember and the first intermediate member comprises a pin and one of aslot and a recess.
 6. A device according to claim 3, wherein the firstintermediate member is directly coupled to a second intermediate member.7. A device according to claim 6, wherein the coupling is by means of apin slidable in a slot or recess.
 8. A device according to claim 6,wherein the locking means is coupled directly to the second intermediatemember.
 9. A device according to claim 6, wherein the secondintermediate member is pivotally mounted.
 10. A device according toclaim 6, wherein the locking means comprises a latch bar movable intoand out of engagement with a corresponding formation on the secondintermediate member.
 11. A device according to claim 2, wherein thelatch means acts directly on the or one of the intermediate members. 12.A device according to claim 1, further comprising manually operablemeans for releasing the locking means.
 13. A device according to claim12, wherein the manually operable means comprise a control memberoperable to move the latch bar.
 14. A device according to claim 13,wherein the control member comprises a Bowden cable.
 15. A deviceaccording to claim 1, wherein the movable member is a pivotal member.16. A device according to claim 15, wherein the pivotal member ismounted on a pivot located in fixed spaced relationship to the rotatablemember.
 17. A device according to claim 15, wherein the loop or noose isanchored to the pivotal member.
 18. A device according to claim 1,wherein the locking means incorporate bias means operable to provide abias force to cause or assist in movement of the movable member.
 19. Adevice according to claim 18, wherein the bias means comprise aresilient member.
 20. A device according to claim 1, wherein the lockingmeans comprise a remotely controllable actuator.
 21. A device accordingto claim 20, wherein the actuator is a solenoid.
 22. A device accordingto claim 20, wherein the actuator controls a latch means operable toprevent the movable member moving.
 23. A device according to claim 1,wherein, when the locking means is disengaged, a force applied to theloop or noose by rotation of the rotatable member in the reversedirection provides a force on the loop or noose to cause the movablemember to move to slacken the loop or noose.
 24. A device according toclaim 23, wherein the loop or noose is maintained in a slack conditionuntil a first rotation of the rotatable member recommences.
 25. A deviceaccording to claim 1, wherein, when the locking means is engaged, themovable member is held in a position such that the rotatable member canfreely rotate in one direction, but as soon as the rotatable memberattempts to rotate in the opposite direction, a force is applied throughthe loop or noose to urge the second member in a direction to cause theloop or noose to tighten on the rotatable member and prevent oppositerotation.
 26. A device according to claim 1, and further comprisingsecond bias means operable to bias the second member to lightly tightenthe loop or noose around the rotatable member.
 27. A device according toclaim 1, wherein the loop or noose passes around a further guide memberbetween the guide member secured to the second member and the pivotalmember, the further guide member being fixed in relation to therotatable member.
 28. A device according to claim 1, wherein a wearmember is carried by the movable member to bear on the rotatable memberand maintain a minimum spacing between the second member and therotatable member.
 29. An anti-roll-back device, comprising a loop ornoose which extends, in use, from an anchor location, around a rotatablemember to another anchor location, and further comprising control meansselectively activatable to put the loop or noose in a first or secondoperative condition wherein, in the first operative condition, therotatable member can rotate in a first forward direction, the loop ornoose tightening on the rotatable member as it attempts to rotate in asecond reverse direction to prevent rotation in the reverse direction,and wherein in the second operative condition the loop or noose allowsthe rotatable member to rotate in the reverse direction, the devicefurther comprising an anchor arrangement located at one of the anchorlocations and operable independently of the operation of the controlmeans to take up slack in the loop or noose arising from stretching ofthe material thereof, the anchor arrangement being lockable to preventthe loop or noose from slackening.
 30. A device according to claim 29,wherein the anchor arrangement comprises a rotatable anchor member towhich the loop or noose is secured, whereby rotation of the anchormember causes part of the loop or noose to be wound on to the anchormember to take up slack.
 31. A device according to claim 30, wherein therotatable anchor member is a pin member.
 32. A device according to claim29, further comprising a resilient member Which provides a force tendingto cause the anchor arrangement to operate to take up slack, whereby anyslack which occurs will automatically be taken up.
 33. A deviceaccording to claim 32, wherein the resilience of the resilient member issufficient to cause the loop or noose to be tightened into light contactwith the rotatable member.
 34. A device according to claim 32, whereinthe resilient member provides a force to a pivotally mounted leverforming part of the anchor arrangement, thereby tending to cause thelever to pivot to operate the anchor arrangement.
 35. A device accordingto claim 29, wherein the operation of the anchor arrangement causesrotation of a ratchet, and the arrangement further comprising a pawlwhich, in use, cooperates with the ratchet to prevent the loop or noosefrom slackening.
 36. A device according to claim 29, wherein the anchorarrangement is adapted to allow manual operation to take up slack.
 37. Adevice according to claim 29, wherein the device further comprises aslidable member slidably mounted in close proximity to the rotatablemember, the loop or noose being anchored to the slidable member andextending around the rotatable member, around a guide member attached tothe slidable member, and to a second anchor location.
 38. A deviceaccording to claim 37, wherein the anchor arrangement is mounted on theslidable member to anchor the loop or noose thereto.